This invention generally pertains to the field of pipe connections. More specifically, the present invention relates to a dual function gasket which is usable in a pipe connection.
The invention is particularly applicable to bell and spigot type joints which include a pipe with a bell end groove in which is received a gasket. However, it will be appreciated by those skilled in the art that the invention has broader applications and may also be adapted for use in many other sealing environments.
Pipes are used for the conveyance of water (or other fluids) under pressure, as in penstocks, inverted siphons, and city water lines. They may also be used as free-flow conduits running partly full, as in drains and sewers. Pipes for conveying water in appreciable quantities have been made of steel, cast iron, concrete, vitrified clay, and most recently, plastic.
It is well-known in the art to extrude plastic pipes in an elongated cylindrical configuration of a desired diameter and then cut the extruded product into individual lengths of convenient size suitable for handling, shipping, and installing. Ten and twenty foot lengths are standard for this type of work. Each length of pipe is enlarged or "belled" at one end sufficiently to join the next adjacent pipe section by receiving in the belled end, the unenlarged or "spigot" end of the adjacent length of pipe. The inside diameter of the bell is formed sufficiently large to receive the spigot end of the next section of pipe with sufficient clearance to allow the application of packing, caulking, gaskets or other seal devices designed to prevent leakage at pipe joints when a plurality of pipe lengths are joined to form a pipeline.
Prior workers in the art, particularly in the plastic pipe industry, have developed various gaskets of suitable design to be retained within an inwardly facing groove formed in the bell. These gaskets were configured to permit the pipe joint to be rapidly made and had the design goal of preventing leakage upon completion of the piping system. Difficulties have, however, been encountered in the formation of a leak tight seal under both pressure and vacuum conditions.
In an effect to solve sealing problems in piping systems, workers in the art have designed gaskets of the type having extending lips which press against the spigot end. Other workers have provided gaskets having peripheral grooves in which are seated locking rings to prevent the movement of the gasket and to retard gasket blow-out when system pressure was applied. Others have attempted to lock the gasket within the annular groove in the bell, for example, by machining the groove to an annular configuration to seal the gasket in the groove or by applying a threaded connection or an adhesive to secure the gasket in place. Such prior art attempts have, however, not proven to be entirely successful.
Sealing problems occur in pipelines for the reason that pipelines are frequently exposed to fairly high pressures. The pressures in a conventional pipeline, and hence on the gaskets, may vary from 0 to 250 psi. The American Water Works Association (AWWA) has set the following standards for pipelines: CIPS or high pressure pipe, such as used for fire hydrants and water mains, must withstand 250 psi; IPS or pressurized pipes, such as regular water supply lines, must withstand 160 psi; PIP or plastic irrigation pipe must withstand 50 psi and sewer pipe must withstand 20 psi.
Most gasket designs have been specifically configured to one of these pressure limitations and economical gaskets which can be used for two or more of these pressure limitations are not generally available. It would be useful, therefore, to have an inexpensively produced gasket which can be selectively configured to provide sealing under various pressure conditions. More specifically, it would be useful to provide a gasket which can be selectively configured to provide sealing under various pressures simply by the addition or removal of a reinforcing ring.
Accordingly, it has been considered desirable to develop a new and improved gasket assembly which would overcome the foregoing difficulties and meet the above stated needs and others while providing better and more advantageous overall results.